A series of studies were undertaken to study the effects of PGE2 and a newly synthesized compound succinylacetone (SA) on the acute and chronic processes of cardiac transplants. Studies were performed in rats and monkeys. An inbred pig colony was used to determine the effect of MHL matching on allograft cardiac survival. The data demonstrate that PGE2 nearly doubles the survival time of transplanted hearts. SA provides indefinite survival of hearts in rats and monkeys when given continuously by an implanted osmotic pump system. These data suggest that a naturally occurring prostaglandin may have adjunctive use for preventing chronic rejection whereas succinylacetone may prove to be a new major immunosuppressive agent for transplantation and avoid the significant complications of cyclosporine A.